1. Field of the Invention
The present invention relates to a metallization process for manufacturing semiconductor devices. More particularly, the invention relates to a method for depositing metal and metal nitride layers by chemical vapor deposition of a precursor.
2. Background of the Related Art
Reliably producing sub-half micron and smaller features is one of the key technologies for the next generation of very large scale integration (VLSI) and ultra large scale integration (ULSI) integrated circuits. However, as the fringes of circuit technology are pressed, the shrinking dimensions of interconnects in VLSI and ULSI technology has placed additional demands on processing capabilities. The multilevel interconnect features that lie at the heart of this technology require careful processing of high aspect ratio features, such as vias, lines, contacts, and other features. Reliable formation of these features is very important to the VLSI and ULSI success and to the continued effort to increase circuit density and quality of individual substrates and die.
As circuit densities increase, the widths of vias, contacts and other features, as well as the dielectric materials between them, decrease to less than one micron dimensions, i.e., 0.25 xcexcm or less, whereas the thickness of the dielectric layers remains substantially constant, with the result that the aspect ratios for the features, i.e., their height divided by width, increases. Many traditional deposition processes have difficulty filling sub-micron structures where the aspect ratio exceed 4:1, and particularly where it exceeds 10:1. Therefore, there is a great amount of ongoing effort being directed at the formation of void-free films for sub-micron features having high aspect ratios.
Conducting metals such as aluminum, copper, and tungsten, are used to fill sub-micron features on substrates during the manufacture of integrated circuits. However, aluminum and copper can diffuse into the structure of adjacent dielectric layers which may form a conductive path and cause device failure. Although, tungsten suffers from less than desirable adhesion to adjacent metal and dielectric layers which may cause the formation of interlayer defects, such as delamination of the tungsten from the patterned substrate, diffusion and less than desirable adhesion may be prevented by depositing a liner layer and/or a barrier layer in a feature before depositing the conducting metal. For conducting metals, the liner layer is preferably composed of a metal that provides good adhesion to the underlying material; and the barrier layer deposited on the liner layer is often a nitride or silicon nitride of that metal which helps protect the underlying material from interlayer diffusion and chemical reactions with subsequently deposited materials.
With the recent progress in sub-quarter-micron copper interconnect technology, tantalum, niobium and the respective nitrides have become popular barrier materials in addition to titanium and titanium nitride. Depending on the application, a diffusion barrier layer may comprise a tantalum or niobium layer, a tantalum nitride or niobium nitride layer, a tantalum/tantalum nitride or niobium/niobium nitride stack or other combinations of diffusion barrier materials. Tantalum, niobium and the respective nitride films have typically been deposited by physical vapor deposition (PVD) and by chemical vapor deposition (CVD) techniques at near atmospheric pressures. However, traditional PVD techniques are not well suited for providing conformal coverage on the wall and bottom surfaces of high aspect ratio vias and other features.
The ability to deposit conformal tantalum and niobium films in high aspect ratio features by the decomposition of organometallic precursors has gained interest in recent years for developing metal organic chemical vapor deposition (MOCVD) techniques. In such techniques, an organometallic precursor gas is introduced into the chamber and caused to decompose, allowing the metal portion thereof to deposit a film layer of the metal on the substrate, and the organic portion of the precursor being exhausted from the chamber. Currently, MOVD techniques deposit films at near atmospheric conditions. However, films deposited at near atmospheric conditions generally have less than desirable coverage of sub-micron features formed on a substrate which can lead to void formation in the substrate features and possible device failure. Further, atmospheric film deposition tends to deposit material on the surfaces of the chamber, which may subsequently flake or delaminate and become a particle problem within the chamber. Particle deposition in the chamber can produce layering defects in the deposited films and provide less than desirable interlayer adhesion.
Additionally, at the present time, there exists only a few commercially available tantalum and niobium precursors, and the precursors that are available produce films that have unacceptable levels of contaminants such as carbon and oxygen, thereby increasing the film""s resistivity and producing films having low diffusion resistance, low thermal stability, and other undesirable film characteristics. Additionally, many precursors, such as for tantalum films, produce nitride films of less than desirable quality and a more effective metal nitride precursor is needed.
The available nitride precursors often produce films that are highly resistive and, in some cases, may be insulative, typically as a result of the inability to control crystalline structure or the chemical structure of the film deposited from the precursor. As the nitrogen content increases in metal films, such as tantalum, the film becomes increasingly resistive, and in the case of a tantalum nitride film, a high nitrogen content will eventually transition a good conducting phase with superior barrier properties, such as Ta2N, to a Ta3N5 insulating phase. In particular, many of the available tantalum nitride precursors readily deposit an insulating Ta3N5 phase. Furthermore, there are no current satisfactory MOCVD techniques and precursors for depositing materials, such as silicon, which can be added to the liner/barrier materials to improve diffusion resistance, chemical resistance, thermal stability or enhance interlayer adhesion.
One problem with depositing liner/barrier schemes using current CVD liner/barrier deposition techniques is that often during substrate processing, it is required to transfer the substrate between processing chambers and/or systems in order to deposit both the metal and metal nitride films. The transfer of substrates between processing chambers and systems increases processing time and decreasing substrate throughput while exposing the films to contamination.
Therefore, there remains a need for forming liner/barrier layers of materials from organometallic precursors with the liner/barrier layers having good interlayer adhesion, higher resistance to diffusion, and greater thermal stability than those produced with prior processes. It would be desirable for the precursors to be deposited in a process by either thermal decomposition or by plasma enhanced decomposition to selectively produce metal and/or metal nitride films that are substantially free of contaminants and have low film resistivities. It would be further desirable if both metal and metal nitride films could be deposited in situ using the same precursor sequentially in the same processing chamber.
The invention generally provides for an organometallic precursor and a method of forming a metal and/or metal nitride on a substrate using the chemical vapor deposition of the organometallic precursor at sub-atmospheric pressures below about 20 Torr. One aspect of the invention provides a thermally decomposable organometallic precursor having the formula:
(Cp(R)n)xMHyxe2x88x92xxe2x80x83xe2x80x83(I)
wherein:
Cp is a cyclopentadienyl functional group,
M is a metal selected from the group consisting of tantalum, vanadium, niobium, and hafnium,
R is an organic group, preferably having at least one carbon-silicon bond,
n is an integer from 0 to 5,
x is a integer from 1 to 4, and
y is the valence of M.
The organic group preferably comprises an alkylsilyl functional group, and most preferably comprises at least three carbon-silicon bonds. The alkyl silyl group may further include at least one silicon-oxygen bond.
In another aspect of the invention, an organometallic precursor of the formula (Cp(R)n)xMHyxe2x88x92x is used process a substrate by depositing a metal or metal nitride film at sub-atmospheric pressures. The method comprises introducing the organometallic precursor into a processing chamber maintained at a pressure of less than about 20 Torr, exposing the organometallic precursor to a processing gas, and decomposing the organometallic precursor to deposit a film. The organometallic precursor may be deposited by a thermal or plasma-enhanced process. The method further comprises exposing the film to a plasma to remove contaminants, densify the film, and reduce the film""s resistivity. In an preferred embodiment, a metal film comprising tantalum is deposited in a processing gas comprising argon, hydrogen, and combinations thereof, and is treated with a the plasma comprising argon, hydrogen, and combinations thereof.
Another aspect of the invention provides a method of depositing a metal/metal nitride liner/barrier layer. The method comprises depositing a metal layer by either a thermal or plasma-enhanced decomposition of an organometallic precursor of the formula (Cp(R)n)xMHyxe2x88x92x in the presence of a processing gas, such as argon or hydrogen, and the metal nitride layer is deposited on the metal layer by the decomposition of an organometallic precursor of the formula (Cp(R)n)xMHyxe2x88x92x in a nitrating reactant gas, such as nitrogen or ammonia (NH3). The same organometallic precursors may be used for the deposition of both the metal and metal nitride layers which may further occur sequentially in the same processing chamber. Alternatively, the organometallic precursor may deposit a metal silicide or metal silicon nitride film by the addition of a silicon containing reactant gas, such as silane, to the processing or reactant gases when decomposing the precursor. To remove contaminants, densify the film, and reduce the film""s resistivity the metal layer (and metal silicide layer) of the liner/barrier layer scheme is preferably exposed to a non-nitrating plasma and the metal nitride layer (and metal silicon nitride layer) may be exposed to either a nitrating or non-nitrating plasma following deposition. For depositing films containing carbon, metal carbon nitride films, may be deposited by foregoing the post deposition plasma treatment.
In another aspect of the invention, a feature is formed on a substrate by depositing a dielectric layer on the substrate, etching a pattern into the substrate, depositing a metal layer on the substrate by the decomposition of an organometallic precursor of the formula (Cp(R)n)xMHyxe2x88x92x in the presence of a processing gas, depositing a metal nitride layer on the substrate by the decomposition of an organometallic precursor of the formula (Cp(R)n)xMHyxe2x88x92x in the presence of a nitrating reactant gas, and depositing a conductive metal layer on the metal nitride layer. Once deposited, the metal layer is preferably exposed to a non-nitrating plasma and metal nitride layer may be exposed to either a nitrating or non-nitrating plasma following the formation of the metal nitride layer on the metal layer. The conductive metal is preferably copper and may be deposited by physical vapor deposition, chemical vapor deposition, or electrochemical deposition, preferably electroplating or electroless deposition.